/Engine/Source/Runtime/SlateCore/Public/Widgets/SWidget.h
Slate may go to sleep when there is no user interaction for some time to save power. However, some UI elements may need to "drive" the UI even when the user is not providing any input (ie, animations, viewport rendering, async polling, etc). A widget notifies Slate of this by registering an "Active Timer" that is executed at a specified frequency to drive the UI. In this way, slate can go to sleep when there is no input and no active timer needs to fire. When any active timer needs to fire, all of Slate will do a Tick and Paint pass.
An active timer handle that can be used to UnRegister later.
[TSharedRef](API\Runtime\Core\Templates\TSharedRef)< FActiveTimerHandle > RegisterActiveTimer ( float TickPeriod, FWidgetActiveTimerDelegate TickFunction )